Infections with Escherichia coli, commonly referred to as colibacillosis, are a major cause of death among birds in the poultry industry. Outbreaks of colibacillosis have been reported in ducks, chickens, and turkeys.
E. coli is subdivided into serological groups based on the antigenic differences of the lipopolysaccharide somatic O, flagellar H and K capsular antigens. More than 170 different O antigens of E. coli have been identified by specific agglutination reactions. In addition, approximately 56 H antigens and over 80 K antigens have been described. Relatively few serological groups of E. coli have been identified in disease outbreaks of colibacillosis. The serological groups usually responsible are 01a:K1; 02a:K1; and 078:K80. Other serological groups less frequently incriminated in disease outbreaks are 03, 06, 08, 011, 015, 022, 055, 074, 088, 095, and 0109.
E. coli is a normal inhabitant of the intestinal tract of most mammals and birds. Birds are continuously exposed to E. coli through contaminated feces, water, feed and other aspects of their environment. Virulent and avirulent strains of E. coli shed into the poultry house environment can survive in dust for periods exceeding 32 weeks in an atmosphere of low humidity. The high concentration of E. coli in the poultry house environment, together with the ability of these bacteria to survive for long periods of time, results in the continuous exposure of birds to potential pathogens.
E. coli is an opportunistic organism causing disease in an already predisposed or immunosuppressed host. Birds become extremely susceptible to respiratory infections of E. coli during primary infections of New castle disease, Mycoplasmosis and Infectious bronchitis. The respiratory tract is the predominant route of exposure leading to clinical infections of E. coli. This is primarily due to inhalation of contaminated dust during periods of low humidity, crowding of birds, and reduced ventilation with excess accumulation of ammonia.
Two forms of E. coli disease are recognized in the poultry industry (i.e., systemic colibacillosis and enteric colibacillosis). However, poultry are normally only affected by the systemic form of colibacillosis, typically after a previous respiratory disease. In systemic colibacillosis, the invading organism passes through the mucosa of the alimentary or respiratory tract and enters the blood stream. This invasion may result in a generalized infection (colisepticaemia) or localized infection.
Respiratory distress and sneezing associated with lesions of the lower respiratory tract are characteristic of colibacillosis. Most deaths occur during the first five days of the disease. The disease has been associated with a number of pathological conditions: Fibrinous pericarditis; perihepatitis; coligranuloma; salpingitis; synovitis; and air-sacculitis.
The control of many bacterial diseases in chickens and turkeys is often accomplished by immunologic intervention with protective vaccines. Both live and inactivated vaccines have been employed in chicken and turkey populations. Attenuated viable organisms have been employed for inducing protection against Mycoplasma gallisepticum, Pasteurella multocida, and Alcaligenes faecalis [H. E. Adler et al., Am. J. Vet. Res., 21, 482-485 (1960); H. E. Adler et al., Avian Dis., 14, 763-769 (1970); I. Hertman et al., Avian Dis., 24, 863-869 (1979); D. S. Burke et al., Avian Dis., 24, 726-733 (1980); A. Michael et al., Avian Dis., 24, 870-877 (1979); A. Michael et al., Avian Dis., 24, 878-884 (1979); J. T. Rice et al., Abstr. in Poultry Sci., 55, 1605 (1976); S. R. Coates et al., Poultry Sci., 56, 273-276 (1977)]. See also U.S. Pat. No. 4,379,140. These attenuated live vaccines have been successfully applied in the drinking water and protect turkeys against intravenous challenge with the homologous serotypes. Inactivated vaccines or bacterins utilizing various adjuvants have been very successful, particularly against such diseases as fowl cholera (P. multocida) and infectious coryza (H. paragallinarum). Monovalent bacterins have been shown to protect against homologous challenge and possibly against heterologous antigens as well [S. R. Coates et al., supra (1977); B. W. Bierer, Poultry Sci., 48, 633-666 (1969); A. Michael et al., Refuah Vet., 33, 117-121 (1976)]. Inactivated E. coli vaccines have been shown to provide protection against systemic challenge, but failed to protect when birds were challenged orally or by the respiratory aerosol method [J. R. Deb et al., Res. Vet. Sci., 24, 308-313 (1978); L. H. Arp, Avian Dis., 24, 808-814 (1980); A. Zanella et al., in Developments in Biological Standardization, Y. Moreau and W. Hennessen, eds., S. Krager, Basel., Vol. 51, pp. 19-32 (1982); J. R. Deb et al., Res. Vet. Sci., 20, 131-138 (1976)].
Immunologic intervention with protective vaccines for the control of colibacillosis in the avian species has met with limited success. The problems in controlling this disease lie partly in determining the factors affecting virulence of strains, colonization, invasiveness, and toxin production [M. M. Levine, in Bacterial Vaccines, R. Germanier, ed., Academic Press, Orlando, Fla., pp. 187-235 (1984); M. M. Levine et al., Microbic. Rev., 47, 510-550 (1983)].
An oral or aerosol vaccine against colibacillosis has several advantages over parental vaccines, including the ease of administration and the lack of adverse side reactions. The ability to colonize the upper nasal mucosa would profoundly influence the immunogenic efficiency of an aerosol vaccine. Since the respiratory tract is the primary entrance site for these pathogenic E. coli organisms, direct stimulation of local secretory antibodies at the portal of entry can enhance immunization against infection in several ways: it would prevent adhesion and colonization of infecting organisms; neutralize toxins; and may have a bactericidal effect, thus inhibiting the systemic entry of E. coli. See S. H. Parry et al., in The Virulence of Escherichia coli, M. Sussman, ed., The Society for General Microbiology, Academic Press, pp. 79-153 (1985); J. H. Darbyshire, in Avian Immunology, A. Toivanen and P. Toivanen, eds., CRC Press, Inc., Vol. 11, pp. 129-161 (1987); J. H. Darbyshire et al., Res. Vet. Sci., 38, 14-21 (1985); J. B. Kaper et al., Vaccine, 6, 197-199 (1987); M. M. Levine et al., Infect. Immun., 23, 729-736 (1979)]. A greater local immune response can be induced using live vaccines as opposed to an inactivated, killed vaccine. This may be due to antigens present on live bacteria that may be absent or altered on inactivated, killed bacteria. However, live vaccines employing mutant strains of bacteria are subject to reversion, thereby resulting in loss of the desired immunologic characteristic.
Because of modern high-density confinement rearing practices and the ubiquitous nature of colibacillosis, it has been extremely difficult to control. The control and prevention of avian colibacillosis has, to a large extent, depended upon proper management practices such as use of pelletized feed, free of fecal contamination; the control of rodent populations; proper ventilation; the use of noncontaminated drinking water; and the control of fecal contamination of hatching eggs. Accordingly, there is a need for a stable live vaccine effective to immunize domestic fowl such as turkeys and chickens against colibacillosis.